[RFC][PATCH 03/11] sched: Robustify preemption leak checks

[Peter Zijlstra]

When we warn about a preempt_count leak; reset the preempt_count to
the known good value such that the problem does not ripple forward.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/exit.c       |    4 +++-
 kernel/sched/core.c |    4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -706,10 +706,12 @@ void do_exit(long code)
 	smp_mb();
 	raw_spin_unlock_wait(&tsk->pi_lock);
 
-	if (unlikely(in_atomic()))
+	if (unlikely(in_atomic())) {
 		pr_info("note: %s[%d] exited with preempt_count %d\n",
 			current->comm, task_pid_nr(current),
 			preempt_count());
+		preempt_count_set(PREEMPT_ENABLED);
+	}
 
 	/* sync mm's RSS info before statistics gathering */
 	if (tsk->mm)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2960,8 +2960,10 @@ static inline void schedule_debug(struct
 	 * schedule() atomically, we ignore that path. Otherwise whine
 	 * if we are scheduling when we should not.
 	 */
-	if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD))
+	if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD)) {
 		__schedule_bug(prev);
+		preempt_count_set(PREEMPT_DISABLED);
+	}
 	rcu_sleep_check();
 
 	profile_hit(SCHED_PROFILING, __builtin_return_address(0));


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